1. Field of the Invention
The present invention relates to a guided travel control apparatus for an unmanned vehicle, and more particularly to a control method and control apparatus to be applied when an unmanned vehicle such as a dump truck is guided to travel to a hopper pit and an earth unloading operation is performed.
2. Description of the Related Art
At operation sites of large-scale mines, an earth unloading operation is performed in which earth is loaded onto an unmanned vehicle such as a dump truck, transported to a hopper pit, and unloaded into the hopper pit. The unmanned vehicle is guided to travel along a traveling course that was taught in advance.
The operation of earth unloading to a hopper pit is performed, as shown in FIG. 1, by rearing vehicles 10 till the rear wheels thereof touch a wheel stopper at the edge of a hopper pit 40 and setting load-carrying platforms (vessels, bodies) 13b so that they interfere with the area of the hopper 40 (load-carrying platforms 13b are positioned above the hopper pit 40). This is done to prevent the earth from scattering around the hopper pit 40 when the load-carrying platforms 13b are tilted and the earth is unloaded.
Therefore, the guided travel has to be preformed with good accuracy so that earth drops reliably onto the hopper pit 40 and that the unmanned vehicle 10 does not get into the hopper pit 40 or get stuck therein during guided travel.
Conventional Technology 1
A teaching method has been conventionally employed by which a traveling course 79 from a start point till an earth unloading point 41 of the hopper pit 40 is actually run prior to the guided travel and positions of various passage points on the traveling course 79 and data relating to advancement direction are acquired as teaching data.
Conventional Technology 2
Japanese Patent Application Laid-open No. 2000-137522 describes an invention according to which position data of a survey line are acquired with an operator-driven vehicle actually traveling along the survey line of an earth unloading site prior to the guided traveling, and teaching data for each traveling course to each target earth unloading point along the survey line are found by computations based on the position data of the survey line.
Conventional Technology 3
International Patent Application WO98/37468 describes an invention according to which when a plurality of unmanned vehicles are guided to travel and there is a risk of interference between a leading unmanned vehicle and a following unmanned vehicle, the following unmanned vehicle waits till the leading unmanned vehicle departs in a position in which the following unmanned vehicle does not interfere with the leading unmanned vehicle, and then the following unmanned vehicle passes through a location where the leading unmanned vehicle was located.
As shown in FIG. 1, a plurality of earth unloading points 41a, 41b, 41c . . . are set around the same hopper pit 40. Further, a plurality of hopper pits 40 are provided in a large-scale operation site. Therefore, with the method of Conventional Technology 1 by which teaching data are acquired by actually traveling along each traveling course till each target earth unloading point is reached, the teaching operation requires significant time, efforts, and skills and greatly decreases the operation efficiency.
Further, due to control errors in guided traveling control (computation processing) and errors caused by slip or the like, a shift occurs between the teaching data relating to the traveling course that was determined in advance and the actual travel trajectory of the unmanned vehicle 10 along the traveling course. In particular, in a location where the unmanned vehicle 10 makes a sharp turn, maximum steering is made during traveling course teaching and teaching data for a minimum turn radius are acquired, thereby making it impossible to correct the aforementioned shift. As a result, the unmanned vehicle 10 gets off the course, cannot continue traveling, and interferes with the hopper pit 40 during traveling, thereby creating a risk of a wheel coming off the unmanned vehicle 10 or the vehicle being stuck in the pit.
Further, in order to increase operation efficiency, as shown in FIG. 1, a plurality of unmanned vehicles 10, 10′, 10″ have to be guided almost simultaneously to travel to the same hopper pit 40 and the earth unloading operation has to be performed almost simultaneously in each earth unloading point 41a, 41b, 41c . . . . 
However, in many cases (see FIG. 1), a traveling course 79 leading to a certain earth unloading point (for example, the earth unloading point 41a) in the vicinity of a hopper pit 40 is unavoidably set close to other earth unloading point (for example, the earth unloading point 41b). Here, when a plurality of unmanned vehicles 10, 10′, 10″ . . . are guided to travel simultaneously, traveling control such that causes an unmanned vehicle that comes close to other vehicle to pass this vehicle or to wait for this other vehicle to pass by is usually conducted in order to avoid interference between the unmanned vehicles. However, if one unmanned vehicle passes other unmanned vehicle in the vicinity of the hopper pit 40, the actual traveling trajectory shifts significantly with respect to the preset traveling course and the target earth unloading point 41a of the hopper pit 40 cannot be accurately reached. Further, where one vehicle waits (stands by) in the vicinity of the hopper pit 40 till the other unmanned vehicle completes the earth unloading operation, the operation efficiency is greatly degraded.
There is also a technology for setting an interference prohibition area in which interference between unmanned vehicles is prohibited and traveling control is performed to prevent the interference of unmanned vehicles in the interference prohibition area (referred to as interference prohibition area avoidance control).
Where such technology of interference prohibition area avoidance control is applied to guided traveling to the hopper pit, the area indicating the hopper pit 40 is set as the interference prohibition area to prevent the unmanned vehicle 10 from interfering with the hopper pit 40 during traveling. However, as described above, in the earth unloading point that is a target ground point of the traveling course, the unmanned vehicle 10 has to be in a state in which part of the vehicle interferes with the area of the hopper pit 40 (load-carrying platform 13b is positioned above the hopper pit 40). As a consequence, if the interference area avoidance control is applied as is, interference of the unmanned vehicle 10 with the hopper pit 40 will be prohibited and the unmanned vehicle 10 will not reach the target earth unloading point. Therefore, the unmanned vehicle 10 has to be caused “to interfere in the interference prohibition area” in the earth unloading point by another method that contradicts the interference area avoidance control. However, presently there is no well-known technology for performing such control.